The present invention relates to the manufacture of tubular products, particularly useful as or for preparing an improved catheter construction. Catheters of the type contemplated are relatively thin and flexible tubes which include inner and outer plastic layers and a wire sheathing embedded therebetween. Generally, the wire sheathing is braided or cross-wound in order to obtain maximum torsional rigidity and a good longitudinal flexibility.
When inserting such a catheter, for instance in a vein, these properties are dicisive, since an easy and reliable insertion will imply firstly that the catheter is able to follow and adapt to the shape of the vein and secondly that the catheter can be rotated about its own axis without being torsionally deformed thereby.
With a view to the insertion, catheters generally also include a hollow plastic tip or distal end in which the wire sheathing has been omitted in order to render the tip more flexible than the remaining part of the catheter.
Previously, the manufacture of such catheters with a flexible plastic tip has been difficult, since the omission of the wire sheathing in the tip or distal end has complicated the manufacture. It is known to prepare catheters of the type contemplated two parts, viz. a tubular body portion with wire sheathing and a separate tip portion without wire sheathing therein.
The body portion is prepared by extruding a first plastic layer onto a core wire, whereafter a relatively tight-fitting wire braid is applied onto this first plastic layer and then a second or outer plastic layer is applied also by extrusion. Finally, pieces of appropriate length are cut from the strand product thus prepared.
Thereafter, or in parallel therewith, tip portions are prepared separately, for instance by extruding a plastic layer having the necessary thickness onto a core wire having the same diameter, and by cutting appropriate pieces therefrom.
Thereafter, a tip portion must be joined to a body portion and this is performed by removing the outer plastic layer on the body portion in such a manner that a portion of the wire braid therein is exposed at one end of the body portion. Thereafter the plastic tip is slipped over the exposed wire braid on the body portion and this will necessitate that one end of the tip portion is expanded in advance by means of a particular tool. Finally, the plastic materials of the end portions thus slipped one over the other are welded or fused together which requires supply of heat and, moreover, pressure must be exerted exteriorly over the joint in order to ensure a completely smooth outer surface.
This way of manufacture is very complicated and time consuming not only due to the necessary joining, but also due to the factthat it is necessary to prepare and handle small pieces separately, namely a tip portion and a body portion for each catheter to be prepared.
Another essential drawback consists in that faulty or incomplete joints are difficult to avoid completely, even with a very careful and comprehensive product control and testing. If such faulty products are to be excluded with an absolute certainty, the check measures necessary to that end will cause a further increase in the product costs.
It is an object of the invention to provide an improved technique whereby tubular products, in particular catheters of the type contemplated can be prepared with substantially lower production costs, with high certainty of faultless products and with a low rejection percentage during the manufacture.
Other objects and advantages of the present invention will become apparent as the description proceeds.